日高変成帯の超塩基性岩II : ウェンザル,パンケヌーシ川地域の超塩基性岩とかんらん石はんれい岩の関係について
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概要
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The ultrabasic rocks of the Hidaka metamorphic belt occur along the western thrust fault and are accompanied closely with the basic igneous rocks. The Wensaru-pankenushi ultrabasic intrusive body is a typical one in this metamorphic belt as well as the Horoman intrusive body described previously by the same authors. This intrusive body is located at the northern part of the metamorphic belt, intruding as a sheet in amphibolites. In this area, the ultrabasic rock is accompanied much closely, though separated with septa of biotite gneiss, with late erogenic basic rocks, especially with olivine gabbro. The ultrabasic body is composed of layered dunite, peridotite and plagioclase peridotite of 50 to 200 m thick, respectively, and their lithologic characteristics are as follows: 1. These rocks show a distinct layered structure (abrupt cryptic layering). 2. Dunite, peridotite and plagioclase peridotite of the lower part of the body may have been recrystallized and are metamorphic in texture. 3. Differentiation values, MgO×100/(MgO+FeO+Fe_2O_3), of the rocks and chemical compositions of minerals do not change with vvarying the rock types. 4. Fe-Mg partition coefficients of coexisting minerals, olivine-clinopyroxene and olivine-orthopyroxene, are not same with those of other alpine-type ultrabasic rocks but with those of ultrabasic nodules in basalts. On the other hand, the characteristics of the olivine gabbro are summerized as follows: 1. A weak layered structure, consisting of the variation of rock-types from more basic to acidic, develops throughout the whole body and especially in the lower part, a distinct rhythmic layering of mafic and femic parts is conspicuous. 2. Differentiation values decrease from the lower to upper part of the body, and Fe of olivine and pyroxenes increases with decrease of the value. 3. Partition coefficients of coexisting olivine and clinopyroxene are same with those of the layered complexes as Skaergaard intrusion. From these evidences of the texture and chemical compositions of rocks and minerals, the ultrabasic rocks and the olivine gabbro have no affinity in their petrological natures, in spite of their intimate connection in occurrence. We will farther research the genetic relation-ships of them.
- 地学団体研究会の論文
- 1967-09-25
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